Friday, 11 November 2011

South side, revisited

To the south of the house, we have a lovely terrace. Actually, it's a slab of concrete covered in scaffolding and deteriorating kenaf board at the moment, but it will soon be a lovely, tiled, terrace, where we can sit out in the sun, or snow.

We need some shade for the downstairs windows, and we need a bit of a balcony upstairs, to hang out washing or futons, or clean windows, so the plan is for a balcony running the whole length of the south wall, sticking about 60 cm out from the house. With some care, it should be possible to get this the right height so there is around 45 degrees from the edge of the balcony to the top of the window, and it will let in every drop of direct winter sunlight until the end of February, and around 60 degrees from the edge of the balcony to the bottom of the window, so it will keep out all the summer sun from the end of April. Upstairs we have shutters that will allow some variation.

This is basic passive solar design, and not really rocket science.
We also would rather not have pillars sticking up in the middle of the terrace, which is in front of the middle window and the kitchen window. This means that some kind of beam needs to cross a span of around 5 metres, with minimal thickness. The idea in the final plan was to put up six pillars around the terrace, one in each corner, and one in the middle next to the bit of wall between the two windows, and another opposite that on the south side of the terrace.

These were all made of wood, and there seemed to be a lot of it. Although I've been demanding a 45 degree line to demarcate no-building zone up and away from the window, the actual results from the Passive House software on how obstacles will reduce incoming sunlight are more subtle.

The best estimate at the moment is that all the windows in the house will lose 2,400 kWh per annum, but they will gain 5,400 kWh in solar gain, so the windows are bringing in 3,000 kWh net, over the winter heating period. In very rough financial terms, we could call this 30,000 yen per annum, if we budget 10 yen for each kWh. This is the thermal output of the windows if we look at them as a heater. Of course windows in Japanese houses usually only work as heaters in the summer, and in the winter they are very effective coolers. They also work as dehumidifiers, turning humidity into condensation on the inside of the glass, and on the frames.

Of course we also got the windows to provide natural light, and to give us a view. Looking at the simple cost benefit of insulation, it would make a lot more sense to have no windows, and use electric light inside, but we don't want to live in a cave.

The house next door to the south, that I've estimated to be five metres tall and 16 metres away, will apparently reduce the amount of heat coming in by almost 300 kWh per annum.  So the house next door has already taken away 10% of this total. 3000 yen per annum.

The amount of heat coming in changes with each adjustment of the windows in or out of the wall, and depending on what we do to each side, above, and to a greater extent in front of them. The passive house software estimates 5% of heat will be lost because the windows are not clean all the time.
I'm assuming that above the ground floor windows, there is a balcony 600 mm higher, sticking out 600 mm. If this comes down by 10 mm, we lose 16 kWh per annum. If, instead, it sticks out another 10 mm from the house, we lose 42 kWh per annum. Only 160 yen or 420 yen per year.

A bigger problem is that the horizontal part of the frame on the south side of the terrace was going to obstruct the sun's rays coming into the house. Around 80 kWh for a 120 mm beam, and 160 kWh for a 240 mm beam. That's 1,600 yen per annum. Over 5%.

So, we're getting rid of the pillars at the south of the terrace, and the wooden frame, and I was thinking about putting a frame of square-section steel on top of six wooden pillars. If it's steel, it should be able to span the five metres above the terrace without needing to be too thick. I was trying to work out the deflection, and it looks like a 150x150 mm beam will only move about a centimetre if I stand in the middle (one Mark is about 125 Newtons). As there are going to be two beams, the frame will move a bit less than this, and should feel solid enough. And anyway, the main job is to provide shade in the summer, and being able to walk along it is a bit of a bonus.
This sounds to be a non-starter though. A steel frame is going to be really heavy, and would need a crane to get it in place. Now that there's a house next door, that would probably mean a big crane to lift it over the whole building. Steel is a lot more expensive than wood, too.
After a little discussion it seems possible to loose the south side pillars and use a bracket from the pillar in the middle of the north side so we don't need a pillar in the middle of the terrace. The beam at the south may be a little thicker, but the effect on solar gain is at least five times less than the beams and pillars at the south sides. It should also cost less.
Another compounding issue is that we want to be able to get some shade over the terrace, probably for most of the summer. If we have some kind of permanent frame, it would be easy to hook up some fabric shading over it. If there is just a balcony, we could get some something like a shop awning that could be extended and retracted more freely, although this could be more expensive and may put a lot of torque on the balcony.

Also, I was wondering about growing vines up the frame, maybe kiwi fruit, which would produce shady leaves in the summer, and just leave branches in the winter. Of course the bare branches would still reduce the thermal gain, and this seems to contradict everything I've said above.
I do like kiwi fruit though. Apparently they have six times the vitamin C of oranges.